Benefits of Knowing Proportions, Its Implications & Research

Over 1.5 billion adults aged 20 and above are considered overweight and obese, which is around 34 percent of the world’s adult population. In fact, health experts say that it will grow to more than 3 billion people by 2023; isn’t that alarming? 

It is really a health necessity to know your weight as it reflects your susceptibility to diseases and illnesses, and the best and easiest way to know your weight condition is by using the body mass index measurement, most commonly known as BMI.

This measurement provides insights about whether your body weight is categorized as healthy, underweight, overweight or obese. You probably have used the BMI measurement as it is generally used in numerous clinics and hospitals all around the world.

What is BMI? 

Basically, the body mass index (BMI) measures a person’s weight in adjustment to their height. It can be calculated through the body weight in kilograms divided by the square of a person’s height in meters (kg/m2). It is a simple, normally inexpensive and noninvasive measure of body fat. 

Though it is widely used to indicate one’s body fat, BMI is only a ‘surrogate measure’. It only measures excess weight rather than the actual excess fat of a person. The term ‘surrogate measure’ means only a substitute for a method. 

However, BMI is still correlated to more direct measures of body fat, including underwater weighing and dual energy x-ray absorptiometry, according to many studies [1].

It is also associated with future health risks; for example, a high BMI predicts future morbidity and death. Hence, BMI is an appropriate measure to screen individuals for obesity and its health risks.

In comparison with other methods, BMI depends solely on an individual’s height and weight, but with access to the proper equipment, a person can have their BMI routinely measured and calculated with reasonable accuracy. 

Ranges of BMI in adults

The body mass index for both adult men and women can be identified as the following according to the World Health Organization [2]: 

• Underweight – adults with BMI less than 18.5. 
• Healthy or normal – the healthy range for BMI in adults is from 18.5 to 24.9. 
• Overweight – adults can be categorized as overweight when their BMI is between 25 to 29.9. 
• Obese – can be defined when BMI is 30 or higher. 

In clinical and research studies, obesity is divided into three categories, such as: 

• Obese Class l – BMI ranges between 30 to 34.9.
• Obese Class II –  BMI ranges between 35 to 39.9.
• Obese Class III – BMI ranges from 40 and above.
• With the continuous growth of extreme obesity, health experts have further divided Class III into super-obesity with a BMI of 50 to 59 and super-super obesity with a 60 BMI.

Based on the calculation and table above, a healthcare professional may advise some significant health and lifestyle changes if your BMI does not fall under the “normal” weight category.

In some countries, health experts have adopted the BMI scale to accurately represent the size and stature of the population. For instance, Asian men and women generally are found to have a higher risk of heart disease at a lower BMI compared with non-Asians. 

The BMI provides an overview of a person’s health for healthcare professionals, based on their weight; however, BMI does not consider other natural factors, including:

• Age
• Sex
• Race
• Genetics
• Fat mass
• Muscle mass
• Bone density

Ranges of BMI for children and teens

There is a separate formula and calculation used for children and teens. The one for adults is not an appropriate measure of weight for children or adolescents.

Moreover, the BMI measurement for children and teens is interpreted differently compared with that for adults. It takes into account the age and sex of the child or teen.

The present BMI charts used for children and teens were developed by the US Centres for Disease Control and Prevention. You can calculate a child’s or teen’s BMI, here: cdc.gov/healthyweight/bmi/calculator.html 

After you put your child’s or teen’s details and get the results, see the following to determine their weight status category. 

• Underweight – children or teens with less than the 5th percentile. 
• Healthy or normal – categorized by 5th percentile to less than the 85th percentile. 
• Overweight – those with 85th to less than the 95th percentile. 
• Obesity – received an equal to or greater than the 95th percentile. 

The categories above are useful for the assessment of weight status in children aged over two years. 

However, BMI charts are only used as a guide to indicate the time to make small lifestyle changes among children and teens, and, of course, when to seek further guidance from healthcare professionals, particularly your physician or a dietitian.

Benefits of knowing body proportions

Determine health risks 

Knowing your BMI is quite useful for doctors to determine your health risks. Your BMI is usually used by healthcare professionals as a biometric marker in regard to your overall health.

Your likelihood of developing chronic illnesses, especially heart disease, anorexia or diabetes, is found to be correlated with having a healthy BMI. Therefore, BMI is used as an effective diagnostic tool [3]. 

It is also used to identify proper assessment for treatment. Moreover, the safety of certain medical procedures generally depends on a person’s BMI if it is within a healthy range, making it easier for surgeons to assess their treatment [4]. 

Guide to health and fitness goals

Determining your BMI allows you to set health and fitness goals. You can customize your health plans based on your BMI to establish realistic goals and increase the likelihood of them from achieving. Some examples are the following:

• For instance, being aware that you have a BMI of 15 may help you make wise decisions like putting more weight on in order to be considered healthy. The best and healthiest route for you to take would be adding a caloric surplus of about 3 to 500 calories every day so you can gain around 3 to 4 pounds every month until you set your BMI into the healthy range.

• Another example is if you have a BMI of 34, which is considered obese, your health priority must be to lose weight. Following a calorie restriction diet of about 500 to 1000 per day and exercising may help you lose between 4 to 10 pounds every month until your BMI goes down to a healthier range.

An objective method

Actually, BMI is not an accurate measurement of body fats as it does not take into account the body’s muscle mass and other extra factors that may add to a person’s abnormal weight. However, one accurate fact for sure is that BMI is objective. 

Objective, in the sense that BMI may indicate your health condition and clearly tell the next step to manage your weight.

You can’t accurately identify by looking at yourself in the mirror that you are underweight or obese, nor the people around you, due to your personal relationships with them and stating the truth may hurt your feelings.

Fortunately, BMI is a scientific method that won’t lie. 

Obesity in the overall population

Collectively speaking, BMI can help in measuring the rates of obesity in a population. As BMI is widely used by many healthcare providers and commonly works for most people, having changes in BMI levels provides an understanding of the ways overweight and obesity differ over time and in between distinct populations [5]. 

Considering that BMI is a relatively simple way to measure obesity in a population, it allows numerous health researchers to easily gather insightful data that they can use to investigate and study the obesity epidemic. 

Healthcare scholars can conveniently look at the relationship between dietary patterns and how they affect the risk of obesity in large groups of individuals. BMI is not prohibitively expensive to measure, in contrast to other body fat measurements.

Small to large groups of researchers can then afford to study larger groups of research subjects to select trends in larger segments of the population.

Implications of BMI 

Body weight is known to be associated with various cardiovascular risk factors. Technically, when BMI increases so as the following: 

• Blood pressure 
• Low-density lipoprotein (LDL) or bad cholesterol
• Triglycerides
• Blood sugar
• Inflammation

The changes in your BMI can be translated into a higher risk of having coronary heart disease, stroke and cardiovascular death.

In fact, people with just a BMI over 21 are at risk of developing health problems, like heart disease and diabetes, and can die early in life. 

Coronary artery disease

Many studies have demonstrated a direct link between unnecessary body weight and CAD or coronary artery disease. 

A meta-analysis of 21 long-term studies that used more than 300,000 subjects for an average of 16 years was conducted. In the study, the participants were overweight and found to have a 32 percent higher risk of developing CAD than those participants who were at a normal weight. Plus, participants who were obese had an 81 percent higher risk [6]. 

Ischemic stroke (blood clots)

Ischemic stroke, caused by blood clots, and coronary artery disease have numerous similarities in terms of disease processes and risk factors. 

In a meta-analysis of over 25 prospective cohort studies with 2.3 million participants, the researchers found a direct, graded link between excess weight and stroke risk [7]. 

Being overweight is found to increase the risk of a person experiencing an ischemic stroke by 22 percent. Meanwhile, obese individuals are 64 percent at risk. 

Also, there was no significant relationship between being overweight or obese and hemorrhagic stroke that is caused by bleeding. 

Cardiovascular death

In a meta-analysis of 26 observational studies that involved 390,000 men and women, some racial and ethnic groups and samples from different countries, it was found that obesity was significantly correlated with death from coronary artery disease and cardiovascular disease. 

Fortunately, weight loss of about 5 to 10 percent of body weight may decrease blood pressure, LDL or bad cholesterol and triglycerides. It can also improve other cardiovascular risk factors [8]. 

Research studies about BMI 

Effects of BMI and perceived health importance

A study was conducted among college students in Taiwan that aims to find the effects of BMI and the perceived importance of health on health behaviors, which include patterns of eating, sleeping and exercising.

The findings of the study emphasize that the increasing importance of health in the perception among college students must be the focal point to help them exercise more regularly [9]. 

Relationship between BMI and healthcare use

In another study, the researchers examined the relationships between BMI and healthcare use with and without undergoing BMI.

Afterward, the research was concluded underpinning previous studies and suggested that interventions to offset the increasing prevalence of overweight and obesity are warranted [10]. 

Association of BMI and mortality

One study that was conducted using the UK population focuses on the association of BMI with overall cause-specific mortality.

The researchers chose to do a cohort research involving 3.6 million adults whose BMI data were collected when they were 16 years old and older. They also conducted subsequent follow-ups that started at whichever the latest data available.

The standard follow-up time period was at the 5th anniversary of the participants’ first BMI record or on January 01, 1998, which is the start date of the death registration data; also, the follow-ups ended when the participants die or on March 8, 2016. 

The study involved exactly 3,632,674 people in the population and the following results were from the analysis of never-smokers, which consisted of 1,969,648 people and 188,057 deaths. 

At the end of the long research, it was concluded that BMI was related to all-cause of death categories, except for transport-related accidents; however, the shape of the association varied. The most causes discovered were cancer, cardiovascular diseases and respiratory diseases. 

In short, BMI has an association with overall mortality and the most specific causes of death. Meanwhile, for mental and behavioral, neurological and external causes, a lower BMI was associated with increased mortality risk [11]. 

Downsides of BMI

As you may have heard, there are medical debates stating that BMI is misleading and inaccurate, and should not be given the merit it is receiving up until now [12].

Hence, let’s look at some of the downsides of using BMI as an indicator of one’s overall health or just as a measurement of body fats alone. 

Does not consider other factors of health

Generally, the concept of BMI only answers yes or no: 

• Does the person have a normal weight? 
• Is he/she obese? 
• Which BMI does she fall into? 

All these possible questions surrounding BMI but it does not take into consideration the following factors:

• Age
• Sex
• Genetics
• Everyday lifestyle
• Medical history
• Some other significant factors affecting one’s weight

When you rely solely on BMI, you may disregard other important measurements of health, such as: 

• Blood sugar
• Blood pressure
• Cholesterol
• Heart rate
• Inflammation levels

As a result, you may overestimate or underestimate your true health status. 

Sex

Furthermore, despite the emphasis on the different natural body compositions of men and women, BMI still promotes the same calculations for both groups. Generally, men are known to have more muscle mass and less fat compared with women [13]. 

Age

Additionally, when a person ages, their body fat mass naturally becomes high and their muscle mass naturally declines. Many studies have shown that a higher BMI of around 23.0–29.9 among older adults can be protective against early death and disease. 

Other important health factors 

Finally, as you use BMI in determining your health, you tend to ignore other aspects of health, such as your mental well-being and complicated sociological factors, including income or earnings, access to an affordable and nutritious diet, food skills and knowledge and living environment.

Assumes all weight is equal

One pound or kilogram of muscle weighs exactly similar to one pound or kilogram of fat. However, muscle is denser and gets less space. With this, a person who is much leaner but has high muscle mass may become heavier on the scale.

For instance, a person with 200 pounds or 97 kilograms with 5 feet 9 inches or 175-centimeter in height has a BMI of 29.5, which can be categorized as overweight in BMI. 

But, two other people of similar height and weight may look completely different. One person can be a bodybuilder with more muscle mass; meanwhile, the other could have higher fat mass.

Does not consider the fat distribution

Having a greater BMI is known to be associated with poorer health outcomes; however, the location of body fat may make a bigger difference.

People with fat stored around their stomach area, or those with android or apple-shaped body types, are found to have a greater risk of chronic disease compared with those with fat stored in their hips, buttocks and thighs, also identified as gynoid or pear-shaped body types. 

In a review of 72 studies that involved data from more than 2.5 million individuals, the researchers discovered that people with apple-shaped fat distribution had significantly higher all-cause mortality risk, while those with pear-shaped fat distribution had a lower risk [14]. 

Actually, the researchers also highlighted that BMI does not consider where fat is located and stored in the body, making it easier to misclassify a person as being unhealthy or at risk of some disease. 

Can lead to weight bias

All medical professionals are expected to use their best and scientifically-based judgment, which they would use the BMI result and consider the patient as a unique individual.

On the negative side, some health professionals only use BMI in order to measure a patient’s health before providing medical advice, which may potentially lead to weight bias and poor quality healthcare [15]. 

People with a higher BMI are usually reported that their doctors focus only on their BMI, despite that their appointment is for an unrelated health concern.

Most of the time, as a result, some serious medical issues may be ignored or are incorrectly looked at as weight-related problems. 

Moreover, many studies presented that the higher one’s BMI is, the less likely they are to attend frequent health checkups with their doctors.

The reason behind this is because of fear of being judged, distrust of the healthcare provider or having to experience negative encounters. It is crucial as it can lead to late diagnoses, treatment and care. 

May not be entirely relevant for all populations

This one also stems back to BMI disregarding other factors affecting health. Many studies have shown that people of Asian descent are at a high risk of chronic disease at lower BMI cut-off points, compared with white people. 

Should we still use BMI?

Following all the downsides mentioned, the answer to this actually depends. 

Some research suggests that using BMI has frequently misclassified metabolic health, which is related to how much fat an individual has and how it is distributed in the body. BMI is also considered unreliable during pregnancy, for athletes and the elderly [16]. 

BMI is a single measure that actually helps in identifying chronic diseases specifically in cardiovascular health or illness; however, it may not be that accurate. This also applies to assessing one’s cholesterol, blood sugar or blood pressure as a single measure. 

For many health experts, the measurement only gives you a snapshot. BMI is just too easy to categorize someone to have a fatal disease. Some health professionals argued that it needs further health assessments.

Furthermore, while cardiovascular health is significant to optimal body function, it is not the only measure of health. 

On a positive note, BMI may be more appropriate in predicting the future rather than current health conditions. For instance, people who are considered healthy and overweight or obese are much more susceptible to developing diabetes or some other negative health consequences over time [17]. 

Several effective assessment tools

BMI has its ups and downs but it is still being used as a primary assessment tool among numerous clinics or hospitals due to it being convenient, cost-effective and accessible in all healthcare settings.

There are other several effective assessment tools that may offer the same function as an indicator of a person’s health.

However, similar to BMI, each of the following assessment tools also comes with its own unique set of advantages and disadvantages. 

1. Waist circumferences

A larger waist circumference may indicate greater body fat in the abdominal area, which is linked to a higher risk of chronic disease. One greater than 35 inches or 85 cm for women and 40 inches or 101.6 cm for men. 

• Benefits – it is easy to measure by only using measuring tape.
• Downsides – it does not consider various body types, including apple-shaped vs. pear-shaped, and builds, such as muscle and bone mass. 

2. Waist-to-hip ratio

A person with a high ratio which is greater than 0.80 for women or greater than 0.95 for men is associated with higher fat stores in the stomach area and a greater risk of heart and chronic disease.

Meanwhile, having a low ratio which is lower than or equal to 0.80 for women or lower than or equal to 0.95 for men suggests higher hip fat storage, which translates to better health.

• Benefits – it is easy to measure by only using measuring tape and a calculator. 
• Downsides – it does not consider various body types, including apple-shaped vs. pear-shaped, and builds, such as muscle and bone mass. 

3. Body fat percentage

The body fat percentage as an assessment tool focuses on the amount of body fat an individual possesses.

• Benefits – it differentiates fat mass and fat-free mass and presents a more accurate representation of health risk compared with BMI.
• Downsides – such convenient assessment tools like skinfold measurements, portable bioelectrical impedance analysis and at-home scales come with a high risk of error.

However, some other accurate tools including dual-energy X-ray absorptiometry, underwater weighing and BodPod are quite expensive and inaccessible for many.

4. Lab tests

Lab tests refer to various blood and vital sign measurements that may indicate chronic disease risks, like blood pressure, heart rate, cholesterol, blood glucose levels and inflammation levels. 

• Benefits – the tests give a more detailed review of one’s metabolic health while not relying only on body fat as a measurement of health.
• Downsides – most of the time, only a single lab value is not enough to diagnose or indicate a health risk.

The bottom line 

Take time to check your physical health, which includes fitness and myriad other health indicators to help you decide the shape that you are in. Using BMI can be a friend that tells you which health choices to make, but of course, initially. 

However, whatever the assessment tool, it is crucial for healthcare professionals not to rely on a single health test or assessment.

A healthcare provider may combine different tools as much as possible, like using BMI with waist circumference, and if a health concern arises, other lab tests may follow.

It is important to consider each patient as an individual with specific healthcare needs to really understand them—physically, mentally, emotionally and spiritually.

[1] https://www.cdc.gov/obesity/downloads/bmiforpactitioners.pdf 
[2]https://www.hsph.harvard.edu/obesity-prevention-source/obesity-definition/obesity-definition-full-story/#references 
[3] https://www.nhlbi.nih.gov/health/educational/lose_wt/risk.htm 
[4] https://pubmed.ncbi.nlm.nih.gov/26263911/ 
[5]  https://www.cdc.gov/obesity/data/adult.html 
[6] https://pubmed.ncbi.nlm.nih.gov/17846390/ 
[7] https://pubmed.ncbi.nlm.nih.gov/20299666/ 
[8] https://www.hsph.harvard.edu/obesity-prevention-source/obesity-consequences/health-effects/
[9] https://www.jmir.org/2020/6/e17640/ 
[10] https://bmchealthservres.biomedcentral.com/articles/10.1186/s12913-019-4577-0 
[11] https://www.sciencedirect.com/science/article/pii/S2213858718302882 
[12] https://www.medicalnewstoday.com/articles/265215 
[13] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4890841/
[14] https://pubmed.ncbi.nlm.nih.gov/32967840/ 
[15] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4381543/ 
[16] https://www.health.harvard.edu/blog/the-link-between-abdominal-fat-and-death-what-is-the-shape-of-health-2021021821960 
[17] https://www.health.harvard.edu/blog/how-useful-is-the-body-mass-index-bmi-201603309339 

Photograph: avanti_photo/Envato